Upstream 6.10.9 does indeed seem to fix it. Half a dozen runs of my reproducers yielded nothing but correct behavior.
Bug#1079394: linux-image-6.10.6-amd64: causes cifs regression, flatpak & ostree signature corruption
- Bug#1079394: linux-image-6.10.6-amd64: causes c... Forest
- Bug#1079394: linux-image-6.10.6-amd64: cau... Forest
- Processed: Re: Bug#1079394: linux-image-6.... Debian Bug Tracking System
- Processed: Re: Bug#1079394: linux-image-6.... Debian Bug Tracking System
- Bug#1079394: linux-image-6.10.6-amd64: cau... Salvatore Bonaccorso
- Bug#1079394: linux-image-6.10.6-amd64:... Salvatore Bonaccorso
- Bug#1079394: linux-image-6.10.6-amd64:... Forest
- Bug#1079394: linux-image-6.10.6-am... Salvatore Bonaccorso
- Bug#1079394: linux-image-6.10.... Forest
- Bug#1079394: linux-image-... Forest
- Bug#1079394: linux-image-6.10.6-amd64:... Forest
- Bug#1079394: marked as done (linux-image-6... Debian Bug Tracking System